Plan sifters of this type are used, in particular, for sifting scrap, semolina- and/or flour-like products in mill process engineering and for sorting various types of vegetable grain such as wheat, rye or maize and generally for separating granular material into different grain sizes.
Plan sifters, in particular large and square plan sifters, belong to the current state of the art, for example for separating and sieving/sifting or classifying ground cereal products.
Operation of a plan sifter is influenced by many factors, natural limits to performance being imposed, even in the best condition. The intensity of the vibrating movement (maximum acceleration) is also restricted both by the moving behaviour of the ground product and by the maximum permitted forces in the housing. Performance data are therefore determined according to the specific quality of the individual fractions.
A square plan sifter is known from WO 93/16815, which has a swinging drive which forces the plan sifter and all sieves to perform a rotating movement, the plan sifter usually being suspended as a whole on rods as a freely vibrating screen.
With these plan sifters, horizontally arranged sieves having different mesh widths are superimposed vertically to form stacks. The sieves are assembled in the form of stacks and are pushed into cupboard-like sieve housings and fixed. The sieve housings are usually arranged symmetrically on either side of an unbalanced drive. The sieve housings form a supporting construction with the base plate and continuous cross bars. The sieve housings are rigidly connected at their front faces to the interposed drive housing via a connecting support. The unbalanced drive can have an unbalanced mass which is connected to the drive shaft at a variable distance as a function of speed (EP-A-491331). According to DE-PS 2823623, the frame of such a plan sifter is designed as a supporting housing which receives and laterally supports the stack of sieves, with a housing base which forms a supporting base for the stack of sieves and on the upwardly directed lateral walls thereof. In a different form, a plan sifter according to DE-PS 2256307 has stack fixing devices which produce vertical forces, the forces of the vibration generator being transmitted via top and bottom elements of rigid stack frames which are resistant to vibration. The stack frames are characterised by two respective vertical elements which are each arranged in a plane containing the centre of gravity of the stack and at right angles to the longitudinal plane extending through the stack and the vibration generator and which are rigidly connected to the top and bottom elements of the stack frames. The vertical elements form the vertical edges of a square vibrating frame, the vibrating bearings of the plan sifter being arranged on these vertical elements.
Although such constructions can sometimes be modular in design, they are expensive to produce.